Plate Tectonics and Volcanoes notes

I. Inside the Earth

• Compositional layers
  • Crust
  • Mantle
  • Core
• Functional layers
  • Lithosphere
  • Aesthenosphere
  • Lower mantle
  • Outer core
  • Inner core

II. Plate Boundaries

• Divergent
• Convergent
  • Subduction
  • Continental collision (suture)
• Transform

III. Plate boundaries and hazards

• Divergent
  • Usually underwater, so no one lives there
  • Above water: volcanoes, small earthquakes, landslides
• Subduction
  • Volcanoes, big earthquakes, landslides, floods
• Suture:
  • Big earthquakes, landslides, floods
• Transform
  • Usually underwater, so no one lives there
  • Above water: big earthquakes

IV. Kinds of lava

• Basalt: thin, runny, ocean floor
• Andesite: thicker, gooier, continental; makes lava flows and explosions
• Rhyolite: thickest, gooiest, most explosive

V. Volcanic hazards

• Lava
  • You can outwalk most lava flows
  • Primary hazard is to structures
  • Don’t build downstream of volcano
• Pyroclastics - broken fragments produced in explosive eruptions (tephra)
  • Bombs: Hardened blob of lava or a chunk of blown-out debris
  • Cinders - smaller material
    • Hazards from large tephra (bombs, cinders): Impact, Burial, Agricultural losses
  • Volcanic ash - shards of glass
    • Hazards from ash fall:
      • Lung damage
      • Mechanical damage
      • Aircraft engines, etc.
      • Burial
      • Agricultural damage
      • Climate change
  • Pyroclastic flows
    • Superheated gas and droplets of magma
    • Rolls downslope as a fluid at high speed and high temperature
    • Mt. Pelee, Mt. Unzen, Krakata
• Mudflows (lahars) - volcanic ash and water
  • Volcanic ash and hot water run downhill as a mudflow
  • Nevado Del Ruiz, November 1985
    • Eruption melts glacier, generates lahars
    • Lahar runs down canyon
    • Village on high ground was spared
    • 23,000 dead as lahar hits Armero, a downstream market town
  • Mt. Rainier:Volcano has significant weathering of large ash deposits, making lahars possible without eruption
  • Sakurajima: erupts almost everyday; has lahar channels to move mudflows around the city
• Gases - CO2, sulfur gases
• Lake Nyos, Cameroon: catastropic CO2 release killed 2500
• The fix: Water pumped up from bottom of lake- spray lets CO2 release into air

VI. Kinds of volcanoes

• Shield: Basaltic lava, broad, gentle slope, quiet lava eruptions
• Stratovolcano (composite): Fuji, Rainier, Hood, Vesuvius
  • Hazards:
    • Lava - andesite/rhyolite
    • Pyroclastics
    • Tephra
    • Ash
    • Pyroclastic flows
    • Mudflows
    • Gases
• Dome
• Rhyolite or andesite
• Often build in crater of stratovolcanoes
• Can be injected along faults
• Tend to build, then explode
• Cinder Cone
  • Can be small independent volcanoes, or found on larger volcanoes
  • Pockets of gas cause small explosions
  • Basalt, andesite, less frequently rhyolite
• Other volcanic features
  • Flood Basalts
  • Caldera

VII. Type of volcano and plate setting

• Shield: Ocean floor - hot spot
• Stratovolcano: Subduction zone
• Cinder cone: Anywhere volcanic activity occurs
• Dome: Subduction, hot spot

VII. Social policy and volcanoes

• Monitoring
  • remote sensing
  • ground deformation
  • seismicity
  • gas
  • hydrology
  • geophysical measurements
• Monitoring issues
  • Who pays?
  • Who initiates?
  • Geopolitical stability
• Managing evacuations
• Managing property loss - volcanic zoning